Lithographic apparatus, device manufacturing method, and device manufactured thereby

ABSTRACT

Apparatus and methods for compensating for the movement of a substrate in a lithographic apparatus during a pulse of radiation include providing an optical structure configured to move a patterned projection beam incident on the substrate in synchronism with the substrate.

RELATED APPLICATIONS

This application claims priority to European Patent Application EP02258164.9, filed Nov. 27, 2002, which document is herein incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to lithographic projection apparatus andmethods.

BACKGROUND

The term “programmable patterning structure” as here employed should bebroadly interpreted as referring to any configurable or programmablestructure or field that may be used to endow an incoming radiation beamwith a patterned cross-section, corresponding to a pattern that is to becreated in a target portion of a substrate; the terms “light valve” and“spatial light modulator” (SLM) can also be used in this context.Generally, such a pattern will correspond to a particular functionallayer in a device being created in the target portion, such as anintegrated circuit or other device (see below). Examples of suchpatterning structure include:

A programmable mirror array. One example of such a device is amatrix-addressable surface having a viscoelastic control layer and areflective surface. The basic principle behind such an apparatus is that(for example) addressed areas of the reflective surface reflect incidentlight as diffracted light, whereas unaddressed areas reflect incidentlight as undiffracted light. Using an appropriate filter, theundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light behind; in this manner, the beam becomespatterned according to the addressing pattern of the matrix-addressablesurface. An array of grating light valves (GLVs) may also be used in acorresponding manner, where each GLV may include a plurality ofreflective ribbons that can be deformed relative to one another (e.g. byapplication of an electric potential) to form a grating that reflectsincident light as diffracted light. A further alternative embodiment ofa programmable mirror array employs a matrix arrangement of very small(possibly microscopic) mirrors, each of which can be individually tiltedabout an axis by applying a suitable localized electric field, or byemploying piezoelectric actuation means. For example, the mirrors may bematrix-addressable, such that addressed mirrors will reflect an incomingradiation beam in a different direction to unaddressed mirrors; in thismanner, the reflected beam is patterned according to the addressingpattern of the matrix-addressable mirrors. The required matrixaddressing can be performed using suitable electronic means. In both ofthe situations described hereabove, the patterning structure cancomprise one or more programmable mirror arrays. More information onmirror arrays as here referred to can be gleaned, for example, from U.S.Pat. Nos. 5,296,891 and No. 5,523,193 and PCT patent applications WO98/38597 and WO 98/33096, which documents are incorporated herein byreference. In the case of a programmable mirror array, the said supportstructure may be embodied as a frame or table, for example, which may befixed or movable as required.

A programmable LCD array. An example of such a construction is given inU.S. Pat. No. 5,229,872, which is incorporated herein by reference. Asabove, the support structure in this case may be embodied as a frame ortable, for example, which may be fixed or movable as required.

It should be appreciated that where pre-biasing of features, opticalproximity correction features, phase variation techniques, and/ormultiple exposure techniques are used, the pattern “displayed” on theprogrammable patterning structure may differ substantially from thepattern eventually transferred to the substrate or layer thereof.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs), flat panel displays, and otherdevices involving fine structures. In such a case, the programmablepatterning structure may generate a circuit pattern corresponding to anindividual layer of, for example, the IC, and this pattern can be imagedonto a target portion (e.g. comprising one or more dies and/orportion(s) thereof) on a substrate (e.g. a glass plate or a wafer ofsilicon or other semiconductor material) that has been coated with alayer of radiation-sensitive material (e.g. resist). In general, asingle wafer will contain a whole matrix or network of adjacent targetportions that are successively irradiated via the projection system(e.g. one at a time).

The lithographic projection apparatus may be of a type commonly referredto as a step-and-scan apparatus. In such an apparatus, each targetportion may be irradiated by progressively scanning the mask patternunder the projection beam in a given reference direction (the “scanning”direction) while synchronously scanning the substrate table parallel oranti-parallel to this direction. Since, in general, the projectionsystem will have a magnification factor M (generally <1), the speed V atwhich the substrate table is scanned will be a factor M times that atwhich the mask table is scanned. A projection beam in a scanning type ofapparatus may have the form of a slit with a slit width in the scanningdirection. More information with regard to lithographic devices as heredescribed can be gleaned, for example, from U.S. Pat. No. 6,046,792,which is incorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (e.g.resist). Prior to this imaging procedure, the substrate may undergovarious other procedures such as priming, resist coating, and/or a softbake. After exposure, the substrate may be subjected to other proceduressuch as a post-exposure bake (PEB), development, a hard bake, and/ormeasurement/inspection of the imaged features. This set of proceduresmay be used as a basis to pattern an individual layer of a device (e.g.an IC). For example, these transfer procedures may result in a patternedlayer of resist on the substrate. One or more pattern processes mayfollow, such as deposition, etching, ion-implantation (doping),metallization, oxidation, chemo-mechanical polishing, etc., each ofwhich may be intended to create, modify, or finish an individual layer.If several layers are required, then the whole procedure, or a variantthereof, may be repeated for each new layer. Eventually, an array ofdevices will be present on the substrate (wafer). These devices are thenseparated from one another by a technique such as dicing or sawing,whence the individual devices can be mounted on a carrier, connected topins, etc. Further information regarding such processes can be obtained,for example, from the book “Microchip Fabrication: A Practical Guide toSemiconductor Processing”, Third Edition, by Peter van Zant, McGraw HillPublishing Co., 1997, ISBN 0-07-067250-4.

The term “projection system” should be broadly interpreted asencompassing various types of projection system, including refractiveoptics, reflective optics, catadioptric systems, and micro lens arrays,for example. It is to be understood that the term “projection system” asused in this application simply refers to any system for transferringthe patterned beam from the programmable patterning structure to thesubstrate. For the sake of simplicity, the projection system mayhereinafter be referred to as the “lens.” The radiation system may alsoinclude components operating according to any of these design types fordirecting, shaping, reducing, enlarging, patterning, and/or otherwisecontrolling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens.”

Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and PCTApplication No. WO 98/40791, which documents are incorporated herein byreference.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index (e.g.water) so as to fill a space between the final element of the projectionsystem and the substrate. Immersion liquids may also be applied to otherspaces in the lithographic apparatus, for example, between the mask andthe first element of the projection system. The use of immersiontechniques to increase the effective numerical aperture of projectionsystems is known in the art.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) andEUV (extreme ultra-violet radiation, e.g. having a wavelength in therange 5–20 nm), as well as particle beams (such as ion beams or electronbeams).

In presently known lithographic projection apparatus using programmablepatterning structure, the substrate table is scanned in the path of thepatterned projection beam (e.g. below the programmable patterningstructure). A pattern is set on the programmable patterning structureand is then exposed on the substrate during a pulse of the radiationsystem. In the interval before the next pulse of the radiation system,the substrate table moves the substrate to a position as required toexpose the next target portion of the substrate (which may include allor part of the previous target portion), and the pattern on theprogrammable patterning structure is updated if necessary. This processmay be repeated until a complete line (e.g. row of target portions) onthe substrate has been scanned, whereupon a new line is started.

During the small but finite time that the pulse of the radiation systemlasts, the substrate table may consequently have moved a small butfinite distance. Previously, such movement has not been a problem forlithographic projection apparatus using programmable patterningstructure, e.g. because the size of the substrate movement during thepulse has been small relative to the size of the feature being exposedon the substrate. Therefore the error produced was not significant.However, as the features being produced on substrates become smaller,such error becomes more significant.

Although specific reference may be made in this text to the use of theapparatus according to an embodiment of the invention in the manufactureof ICs, it should be explicitly understood that such an apparatus hasmany other possible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display (LCD)panels, thin-film magnetic heads, thin-film-transistor (TFT) LCD panels,printed circuit boards (PCBs), DNA analysis devices, etc. The skilledartisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” in this text shouldbe considered as being replaced by the more general terms “substrate”and “target portion”, respectively.

SUMMARY

A device manufacturing method according to an embodiment of theinvention includes using a radiation system to provide a pulsed beam ofradiation, and using a patterning structure to pattern the pulsed beamaccording to a desired pattern. The patterned beam is projected onto atarget portion of a layer of radiation-sensitive material that at leastpartially covers a substrate, and the substrate is moved relative to theprojection system. A path of the projected beam relative to theprojection system is altered during at least one pulse of the pulsedbeam, such that a cross-section of the projected beam in a planeparallel to a surface of the target portion is substantially stationaryrelative to the substrate during the at least one pulse. Severalapparatus that may be applied to perform such a method, and devicesmanufactured thereby, are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying schematic drawings inwhich:

FIG. 1 depicts a lithographic projection apparatus according to anembodiment of the invention;

FIG. 2 depicts a structure configured to move the patterned projectionbeam according to an embodiment of the present invention;

FIG. 3 depicts a structure configured to move the patterned projectionbeam according to a second embodiment of the present invention;

FIG. 4 depicts a structure configured to move the patterned projectionbeam according to a third embodiment of the present invention; and

FIG. 5 depicts a variant of the structure shown in FIG. 4.

In the Figures, corresponding reference symbols indicate correspondingparts.

DETAILED DESCRIPTION

Embodiments of the invention include, for example, methods and apparatusthat may be used to reduce errors caused by movement of the substrateduring a pulse of the radiation system.

FIG. 1 schematically depicts a lithographic projection apparatusaccording to a particular embodiment of the invention. The apparatuscomprises:

A radiation system configured to supply (e.g. having structure capableof supplying) a projection beam of radiation. In this particularexample, the radiation system Ex, IL, for supplying a projection beam PBof radiation (e.g. UV or EUV radiation) also comprises a radiationsource LA;

A programmable patterning structure PPM (e.g. a programmable mirrorarray) configured to apply a pattern to the projection beam. In general,the position of the programmable patterning structure will be fixedrelative to item PL. However, it may instead be connected to apositioning structure configured to accurately position it with respectto item PL;

An object table (substrate table) configured to hold a substrate. Inthis example, substrate table WT is provided with a substrate holder forholding a substrate W (e.g. a resist-coated semiconductor wafer) and isconnected to a positioning structure for accurately positioning thesubstrate with respect to item PL and (e.g. interferometric) measurementstructure IF, which is configured to accurately indicate the position ofthe substrate and/or substrate table with respect to lens PL; and

A projection system (“lens”) PL (e.g. a quartz and/or CaF₂ lens system,a catadioptric system comprising lens elements made from such materials,and/or a mirror system) configured to project the patterned beam onto atarget portion C (e.g. comprising one or more dies and/or portion(s)thereof) of the substrate W. The projection system may project an imageof the programmable patterning structure onto the substrate;alternatively, the projection system may project images of secondarysources for which the elements of the programmable patterning structureact as shutters. The projection system may also comprise a micro lensarray (MLA), e.g. to form the secondary sources and to projectmicrospots onto the substrate.

As here depicted, the apparatus is of a reflective type (e.g. has areflective programmable patterning structure). However, in general, itmay also be of a transmissive type (e.g. with a transmissiveprogrammable patterning structure) or have aspects of both types.

The source LA (e.g. a mercury lamp, an excimer laser, an electron gun, alaser-produced plasma source or discharge plasma source, or an undulatorprovided around the path of an electron beam in a storage ring orsynchrotron) produces a beam of radiation. This beam is fed into anillumination system (illuminator) IL, either directly or after havingtraversed a conditioning structure or field, such as a beam expander Ex,for example. The illuminator IL may comprise an adjusting structure orfield AM for setting the outer and/or inner radial extent (commonlyreferred to as σ-outer and σ-inner, respectively) of the intensitydistribution in the beam, which may affect the angular distribution ofthe radiation energy delivered by the projection beam at, for example,the substrate. In addition, the apparatus will generally comprisevarious other components, such as an integrator IN and a condenser CO.In this way, the beam PB impinging on the mask MA has a desireduniformity and intensity distribution in its cross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g. withthe aid of suitable direction mirrors); this latter scenario is oftenthe case when the source LA is an excimer laser. The current inventionand claims encompass both of these scenarios.

The beam PB subsequently intercepts the programmable patterningstructure PPM, which may be held on a mask table. Having beenselectively reflected by (alternatively, having traversed) theprogrammable patterning structure PPM, the beam PB passes through thelens PL, which focuses the beam PB onto a target portion C of thesubstrate W. With the aid of the positioning structure (andinterferometric measuring structure IF), the substrate table WT can bemoved accurately, e.g. so as to position different target portions C inthe path of the beam PB. Where used, a positioning structure for theprogrammable patterning structure PPM can be used to accurately positionthe programmable patterning structure PPM with respect to the path ofthe beam PB (e.g. after a placement of the programmable patterningstructure PPM, between scans, and/or during a scan).

In general, movement of the object table WT may be realized with the aidof a long-stroke module (e.g. for coarse positioning) and a short-strokemodule (e.g. for fine positioning), which are not explicitly depicted inFIG. 1. A similar system may be used to position the programmablepatterning structure PPM. It will be appreciated that, to provide therequired relative movement, the projection beam may alternatively oradditionally be moveable, while the object table and/or the programmablepatterning structure PPM may have a fixed position. Programmablepatterning structure PPM and substrate W may be aligned using substratealignment marks P, P2 (possibly in conjunction with alignment marks ofthe programmable patterning structure PPM).

The depicted apparatus can be used in several different modes. In onescan mode, the mask table MT is movable in a given direction (theso-called “scan direction”, e.g. the y direction) with a speed v, sothat the projection beam PB is caused to scan over a mask image.Concurrently, the substrate table WT is simultaneously moved in the sameor opposite direction at a speed V=Mv, in which M is the magnificationof the lens PL (typically, M=¼ or ⅕). In this manner, a relatively largetarget portion C can be exposed, without having to compromise onresolution.

In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning structure, and the substrate table WTis moved or scanned while a pattern imparted to the projection beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning structureis updated as required after each movement of the substrate table WT orin between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning structure, such as a programmable mirror arrayof a type as referred to above.

Combinations and/or variations on the above-described modes of use orentirely different modes of use may also be employed.

An apparatus as depicted in FIG. 1 may be used, for example, in thefollowing manner. In pulse mode, the programmable patterning structureis kept essentially stationary, and the entire pattern is projected ontoa target portion C of the substrate using a pulsed radiation source. Thesubstrate table WT is moved with an essentially constant speed such thatthe projection beam PB is caused to scan a line across the substrate W.The pattern on the programmable patterning structure is updated asrequired between pulses of the radiation system, and the pulses aretimed such that successive target portions C are exposed at the requiredlocations on the substrate. Consequently, the projection beam can scanacross the substrate W to expose the complete pattern for a strip of thesubstrate. Such a process may be repeated until the complete substratehas been exposed line by line. Different modes may also be used.

An apparatus according to one embodiment of the invention includes alayer of electro-optical material through which the patterned projectionbeam passes. A control system may be provided to apply a control voltageacross the electro-optical material, thereby changing the birefringenceof the electro-optical material. The change in birefringence of theelectro-optical material in response to changes in the control voltagemoves the part of the patterned projection beam emitted from it that ispolarized in a given direction. Therefore the patterned projection beammay be polarized such that all of the patterned projection beam is movedby changes in the birefringence of the electro-optical material.

FIG. 2 shows, schematically, an apparatus according to such anembodiment that may be applied to shift a patterned projection beam. Asshown, the patterned projection beam 2 passes through a polarizingfilter 3. The patterned projection beam then passes through a layer ofelectro-optical material 4. A voltage V applied to the electro-opticalmaterial 4 changes its birefringence as required. When no voltage isapplied, the patterned projection beam follows the path denoted 5. Whena voltage is applied to the electro-optical material 4 the patternedprojection beam is shifted to the path denoted 6.

The optical axis of the electro-optical material 4 is oriented such thatthe polarized projection beam is shifted by the birefringence of theelectro-optical material 4. The shift S produced by applying a voltageto the electro-optical material 4 can be determined by the followingequation: $\begin{matrix}{S = {{d \cdot \sin}\;{\alpha \cdot \cos}\;{\alpha \cdot \left( {\frac{1}{\sqrt{n_{1}^{2} - {\sin^{\,^{2}}\alpha}}} - \frac{1}{\sqrt{n_{0}^{2} - {\sin^{\,^{2}}\alpha}}}} \right)}}} & \lbrack 1\rbrack\end{matrix}$

where d is the thickness of the layer of electro-optical material, α isthe angle between the patterned projection beam and the surface of theelectro-optical material, N₀ is the ratio of the refractive index of theenvironment in which the apparatus functions to the refractive index ofthe electro-optical material when no voltage is applied and n₁ is thecorresponding ratio of the refractive indices when a given voltage hasbeen applied to the electro-optical material. Consequently, as thevoltage applied to the electro-optical material is changed, the shift Schanges. By applying a gradually changing voltage, the patternedprojection beam can be caused to gradually shift. By applying anappropriately shaped signal to the electro-optical material, thepatterned projection beam can be caused to scan in synchronism with thesubstrate as it moves during the short time of a pulse of the radiationsystem. Consequently, errors in the placement of features on thesubstrate may be reduced.

Although as here shown the patterned projection beam 2 is polarized bymeans of a polarizing filter 3, this need not be the case. Inparticular, the patterned projection beam 2 may already be polarized,for example, as a result of the programmable patterning means or becausethe radiation source inherently produces polarized radiation.

The electro-optical layer may be formed from one or more of anywell-known electro-optical materials, such as ADP (ammonium dihydrogenphosphate), AD*P (deuterated ADP), KDP (potassium dihydrogen phosphate),and KD*P (deuterated KDP). In order to obtain the best response from theelectro-optical material, it is preferably operated close to, but above,the Curie temperature of the material used. The Curie temperature isgenerally lower than the ambient temperature for the apparatus. The KDPfor example has a Curie temperature of 123 K, KD*P has a Curietemperature variously reported as 213 or 222 K and ADP has a Curietemperature of 148 K. Consequently a temperature controlled cooling unit(not shown) may be provided to cool the electro-optical layer.

After traversing the electro-optical material, the patterned projectionbeam may then be passed through a quarter wavelength plate 7, forexample, to circularly polarize the patterned projection beam ifrequired. Alternatively, the patterned projection beam may remainlinearly polarized or may be de-polarized.

FIG. 3 shows an apparatus according to an alternative embodiment of thepresent invention. This embodiment is similar to the first embodiment,and the description of corresponding features will not be repeated. Inthis apparatus, a second layer of electro-optical material 8 is providedin the path of the patterned projection beam. The second layer 8, whichmay include one or more of the electro-optical materials describedabove, is oriented differently than the first layer 4. For example, thedirection of the optical axis of the second layer 8 may be differentfrom (e.g. perpendicular to) the direction of the optical axis of thefirst layer. Consequently, when a voltage V is applied to the firstlayer 4, radiation in the patterned projection beam that is polarized ina first direction is shifted and when a voltage V′ is applied to thesecond layer 8 (e.g. changing its birefringence), radiation that ispolarized in a second (e.g. orthogonal) direction is shifted. Therefore,by simultaneously applying appropriate voltages V, V′ to both layers ofelectro-optical material 4, 8 the entire patterned projection beam 2 maybe shifted, without the need for it to be polarized.

The shift produced by the second layer 8 of electro-optical material canbe determined using Equation 1 given above. Some calibration may berequired to ensure that both polarizations of the radiation are shiftedby the same amount. For example, slight differences in the thicknessesD, D′ of the two layers of electro-optical material 4, 8 can becompensated for by adjustments of voltage V and/or voltage V′. It hasbeen found that a 7 kV voltage change across a layer of electro-opticalmaterial of 0.7 mm thickness produces a 50 nm shift.

An alternative embodiment of the invention includes a reflective surfaceconfigured to move the patterned projection beam relative to theprojection system. For example, the reflective surface may be mountedsuch that the angle between the surface and the patterned projectionbeam incident on it can vary during the pulse of the radiation system.As the angle changes, so the position of the beam reflected from it ismoved.

FIG. 4 shows an apparatus according to such an embodiment of the presentinvention. In this case, a rotating prism 15 having a polygonalcross-section is applied to shift the patterned projection means 2.Prism 15, here shown in cross section, may be located in the back focalplane of the lithographic apparatus. The prism has a plurality of faces16 that are reflective to the patterned projection beam 2, such that theedge faces form a reflective surface. As the prism rotates, each face inturn reflects the patterned projection beam. Whilst the patternedprojection beam is incident on each face, the angle of each facerelative to the patterned projection beam changes.

FIG. 4 also shows an application of the apparatus at a first time point,when the prism 15 is in a first position, and at a second time point,when the prism 15′ is in a second position. As the prism rotates, theangle at which the patterned projection beam 2 is incident on thereflective face 16 of the prism changes. Correspondingly, the angle atwhich the patterned projection beam 5, 6 radiates from the reflectiveface 16 also changes. As shown, the difference in angles between thereflected patterned projection beam 5 at the first time point and thereflected patterned projection beam 6 at the second time point producesa shift S where the patterned projection beam is incident on thesubstrate. By careful timing of the rotation of the prism 15 withrespect to the pulse frequency of the radiation system and correctselection of the size of the prism, the patterned projection beam 2 canbe made to scan in synchronism with the moving substrate for theduration of a pulse of radiation. In the interval between pulses ofradiation, the prism 15 rotates to present a different face 16 at thestart of the subsequent pulse of the radiation system. Potentialadvantages of systems including apparatus according to this embodimentmay include that polarization of the patterned projection beam is notrequired and that the apparatus may be used in a lithographic projectionapparatus that solely uses reflective components.

Alternatively, a transparent rotating prism 25 may be used, as shown inFIG. 5. In this case, the prism may be located in the imaging plane.

Errors caused by the movement of the substrate relative to theprojection system during a pulse of radiation may be reduced byproviding one or more apparatus to shift the patterned projection beamin synchronism with the movement of the substrate during a pulse ofradiation, which may allow the projection beam to remain more accuratelyaligned on the substrate. Alternative structures that may be applied toshift the patterned projection beam are also within the scope of theinvention.

It may be desirable to move the substrate at a constant velocityrelative to the projection system during a series of pulses of theradiation system and the intervals in between the pulses. An apparatusas described herein may then be used to move the patterned projectionbeam in synchronism with the movement of the substrate for the durationof at least one pulse of the radiation system. Having the substratemoving at a constant velocity may reduce the complexity of the substratetable and the positional drivers associated with it, and moving thepatterned projection beam in synchronism with the movement of thesubstrate may reduce consequent errors.

The patterned projection beam may be moved in synchronism with themovement of the substrate during a plurality of pulses. Such anarrangement may enable the images of the programmable patterningstructure to be projected onto the same part of the substrate aplurality of times. This technique may be done, for example, if theintensity of the pulse of the patterned projection beam is notsufficient to produce a complete exposure on the substrate. Moving thepatterned projection beam in synchronism with the substrate may reducethe occurrence of overlay errors between subsequent exposures of thepattern on the substrate.

Successive patterns on the programmable patterning structure that areexposed on the substrate by each pulse may be different. For example,corrections may be made in subsequent pulses to offset errors in a firstpulse. Alternatively, changes in the pattern may be used to produce grayscale images for some of the features (for example, by only exposingthose features for a proportion of the total number of pulses imagedonto a given part of the substrate).

Additionally (or alternatively) the intensity of the patternedprojection beam, the illumination of the programmable patterning means,and/or the pupil filtering may be changed for one or more of the pulsesof the radiation system that are projected onto the same part of thesubstrate. This technique may be used, for example, to increase thenumber of gray scales that may be generated using the techniquedescribed in the preceding paragraph or may be used to optimisedifferent exposures for features oriented in different directions.

Whilst specific embodiments of the invention have been described above,it will be appreciated that the invention as claimed may be practicedotherwise than as described. For example, although use of a lithographyapparatus to expose a resist on a substrate is herein described, it willbe appreciated that the invention is not limited to this use, and anapparatus according to an embodiment of the invention may be used toproject a patterned projection beam for use in resistless lithography.Thus, it is explicitly noted that the description of these embodimentsis not intended to limit the invention as claimed.

1. A lithographic projection apparatus comprising: a radiation systemconfigured to provide a pulsed beam of radiation; a programmablepatterning structure configured to pattern the pulsed beam according toa desired pattern; a projection system configured to project thepatterned beam onto a target portion of a substrate; a positioningstructure configured to move the substrate relative to the projectionsystem during exposure by the patterned beam; and an optical structureconfigured to move the projected beam relative to the projection systemduring at least one pulse of the pulsed beam such that the projectedbeam is shifted in synchronism with the movement of the substrate duringsaid at least one pulse.
 2. The lithographic projection apparatusaccording to claim 1, wherein the positioning structure is configured tomove the substrate at a substantially constant velocity relative to theprojection system during the course of a plurality of pulses of theradiation system and the intervals therebetween, and wherein theprojected beam is moved in synchronism with the movement of thesubstrate for the duration of at least one pulse of the pulsed beam. 3.The lithographic projection apparatus according to claim 1, wherein theprojected beam is moved in synchronism with the movement of thesubstrate during a plurality of pulses of the pulsed beam such that apattern of the programmable patterning structure is projected ontosubstantially the same place on the substrate a plurality of times. 4.The lithographic projection apparatus according to claim 3, wherein aconfiguration of the programmable patterning structure is changedbetween the plurality of projections onto substantially the same placeon the substrate.
 5. The lithographic projection apparatus according toclaim 3, wherein at least one of an intensity of the projected beam, anillumination of the programmable patterning structure, and a pupilfiltering are changed for at least one of the plurality of projectionsonto substantially the same place on the substrate.
 6. The lithographicprojection apparatus according to claim 1, wherein said opticalstructure comprises: a layer of electro-optical material arranged in apath of the projected beam; and a control system configured to apply acontrol voltage across at least a portion of the layer ofelectro-optical material, wherein a birefringence of the electro-opticalmaterial of the layer varies according to a voltage across the material.7. The lithographic projection apparatus according to claim 6, whereinthe apparatus is configured such that the projected beam is polarized,and wherein an optical axis of the layer of electro-optical material isoriented such that substantially all of the projected beam is moved. 8.The lithographic projection apparatus according to claim 6, wherein saidoptical structure further comprises a second layer of electro-opticalmaterial arranged in a path of the projected beam and across at least aportion of which the control system configured to apply a second controlvoltage, wherein a birefringence of the electro-optical material of thesecond layer varies according to a voltage across the material, andwherein a direction of an optical axis of the second layer ofelectro-optical material is substantially perpendicular to a directionof an optical axis of the first layer, such that changing thebirefringence of both layers moves substantially all of the projectedbeam.
 9. The lithographic projection apparatus according to claim 1,wherein said optical structure comprises a reflective surface mountedsuch that an angle between the surface and the projected beam incidentupon it varies during a pulse of the pulsed beam.
 10. The lithographicprojection apparatus according to claim 9, wherein said opticalstructure comprises a rotating prism having a plurality of edge faces,and wherein at least one edge face is the surface on which the patternedprojection beam is incident during the pulse of the pulsed beam.
 11. Thelithographic projection apparatus according to claim 1, wherein saidoptical structure comprises an element that is transmissive to the beamof radiation, mounted such that an angle between the projected beam anda surface of the transmissive element on which it is incident variesduring a pulse of the pulsed beam.
 12. The lithographic projectionapparatus according to claim 11, wherein said optical structurecomprises a rotating prism having a plurality of edge faces, and whereinat least one edge face is the surface on which the patterned projectionbeam is incident during the pulse of the pulsed beam.
 13. A devicemanufacturing method, said method comprising: using a radiation systemto provide a pulsed beam of radiation; using a patterning structure topattern the pulsed beam according to a desired pattern; projecting thepatterned beam onto a target portion of a layer of radiation-sensitivematerial that at least partially covers a substrate; moving thesubstrate relative to the projection system during exposure by thepatterned beam; and moving the projected beam relative to the projectionsystem during at least one pulse of the pulsed beam such that theprojected beam is shifted in synchronism with the movement of thesubstrate during said at least one pulse.
 14. A lithographic projectionapparatus comprising: a radiation system configured to provide a pulsedbeam of radiation; a programmable patterning structure configured topattern the pulsed beam according to a desired pattern; a projectionsystem configured to project the patterned beam onto a target portion ofa substrate; a positioning structure configured to move the substraterelative to the projection system during exposure by the patterned beam;and an optical structure configured to alter a path of the projectedbeam relative to the projection system during at least one pulse of thepulsed beam such that a cross-section of the projected beam in a planeparallel to a surface of the target portion is shifted in synchronismwith the movement of the substrate during said at least one pulse. 15.The lithographic projection apparatus according to claim 14, whereinsaid optical structure comprises: a layer of electro-optical materialarranged in a path of the projected beam; and a control systemconfigured to vary a birefringence of at least a portion of the layer ofelectro-optical material according to a control voltage.
 16. Thelithographic projection apparatus according to claim 14, wherein saidoptical structure further comprises a second layer of electro-opticalmaterial arranged in a path of the projected beam and across at least aportion of which the control system configured to apply a second controlvoltage, wherein the control system is further configured to vary abirefringence of at least a portion of the second layer ofelectro-optical material according to a second control voltage, andwherein a direction of an extraordinary axis of the second layer ofelectro-optical material is substantially perpendicular to a directionof an extraordinary axis of the first layer.
 17. The lithographicprojection apparatus according to claim 14, wherein said opticalstructure comprises a reflective surface mounted such that an anglebetween the surface and the projected beam incident upon it variesduring a pulse of the pulsed beam.
 18. The lithographic projectionapparatus according to claim 17, wherein said optical structurecomprises an element that is transmissive to the beam of radiation,mounted such that an angle between the projected beam and a surface ofthe transmissive element on which it is incident varies during a pulseof the pulsed beam.
 19. A device manufacturing method, said methodcomprising: using a radiation system to provide a pulsed beam ofradiation; using a patterning structure to pattern the pulsed beamaccording to a desired pattern; projecting the patterned beam onto atarget portion of a layer of radiation-sensitive material that at leastpartially covers a substrate; moving the substrate relative to theprojection system during exposure by the patterned beam; and altering apath of the projected beam relative to the projection system during atleast one pulse of the pulsed beam such that a cross-section of theprojected beam in a plane parallel to a surface of the target portion isshifted in synchronism with the movement of the substrate during said atleast one pulse.
 20. The device manufacturing method according to claim19, wherein altering a path of the projected beam includes altering thepath in synchronism with said moving the substrate during a plurality ofpulses of the pulsed beam, such that the desired pattern is projectedonto substantially the same place on the target portion a plurality oftimes.
 21. The device manufacturing method according to claim 20,wherein a configuration of the programmable patterning structure ischanged between the plurality of projections onto substantially the sameplace on the substrate.